Ketimine structure-containing organoalkoxysilanes are characterized by the fact that the ketimine group is by itself inert to reaction, but reacts readily with water, resulting in decomposition into a monocarbonyl compound and an amino-functional alkoxysilane that contains a highly reactive primary amino group. Ketimine structure-containing organoalkoxysilanes are therefore characterized by an excellent storage stability in the absence of moisture and are useful as adhesion improvers and curing agents for a variety of curable resins and primers.
Dehydration condensation between an amino-functional alkoxysilane and a monocarbonyl compound is described in U.S. Pat. No. 2,942,019 as a method for producing ketimine structure-containing organoalkoxysilane. In this method, however, the alkoxy group undergoes partial hydrolysis and condensation due to the water by-product, resulting in the production of oligomer, that is, organopolysiloxane with a low degree of polymerization (hereinafter DP). This has resulted in a reduced purity for the ketimine structure-containing organoalkoxysilane.
In order to solve this problem, a method is described in Japanese Laid Open Patent Application Number (hereinafter Kokai) Hei 03-263421 in which the water by-product is azeotropically distilled out using a nonpolar organic solvent. A problem with this method has been that the reaction does not go to completion, resulting in large residual amounts of highly reactive amino-functional silane.
A method is described in Kokai Hei 7-247295 in which the water is removed by the addition of a dehydrating agent such as molecular sieve or magnesium sulfate. With this method, however, it has been necessary to run the reaction at low temperatures since water adsorption and desorption are equilibrium reactions, which has resulted in a poor efficiency. Moreover, the alkoxy group undergoes partial hydrolysis and condensation, resulting in a tendency for oligomer to be produced and causing the problem of a low purity for the ketimine structure-containing organoalkoxysilane.
Kokai Hei 7-247294 and 2000-44817 (equivalent to EP096771) describe a method in which the water fraction is azeotropically distilled out while amino-functional alkoxysilane is added dropwise to the heated monocarbonyl compound. However, it has also been difficult with this method to obtain a high-purity ketimine structure-containing organoalkoxysilane product. Particularly in the case of a ketimine structure-containing organoalkoxysilane that bears a highly hydrolyzable alkoxy group such as methoxy, partial hydrolysis and condensation of the methoxysilane with concomitant oligomer production has made it necessary to proceed through an additional distillative purification step in order to raise the purity of such a ketimine structure-containing organoalkoxysilane.